Preclinical characterization of a (S)-N-(4-cyano-3-trifluoromethyl-phenyl)-3-(3-fluoro, 4-chlorophenoxy)-2-hydroxy-2-methyl-propanamide: a selective androgen receptor modulator for hormonal male contraception

Abstract

The pharmacologic effects of (S)-N-(4-cyano-3-trifluoromethyl-phenyl)-3-(3-fluoro, 4-chlorophenoxy)-2-hydroxy-2-methyl-propanamide (S-23) were characterized in male rats as an animal model of hormonal male contraception. S-23 showed high binding affinity (inhibitory constant = 1.7 +/- 0.2 nm) and was identified as a full agonist in vitro. In castrated male rats, the ED50 of S-23 in the prostate and levator ani muscle was 0.43 and 0.079 mg/d, respectively. In intact male rats treated for 14 d, S-23 alone suppressed LH levels by greater than 50% at doses greater than 0.1 mg/d, with corresponding decreases in the size of the prostate but increases in the size of levator ani muscle. In intact male rats treated for up to 10 wk with S-23 and estradiol benzoate (EB; necessary to maintain sexual behavior in rats), S-23 showed biphasic effects on androgenic tissues and spermatogenesis by suppressing serum concentrations of LH and FSH. EB alone showed no effect on spermatogenesis. In the EB + S-23 (0.1 mg/d) group, four of six animals showed no sperm in the testis and zero pregnancies (none of six) in mating trials. After termination of treatment, infertility was fully reversible, with a 100% pregnancy rate observed after 100 d of recovery. S-23 increased bone mineral density and lean mass but reduced fat mass in a dose-dependent manner. This is the first study to show that a selective androgen receptor modulator combined with EB is an effective and reversible regimen for hormonal male contraception in rats. The beneficial effects of S-23 on the muscle, tissue selectivity, and favorable pharmacokinetic properties make it a strong candidate for use in oral male contraception.

Figure 1

Chemical structures, AR binding affinity, and in vitro transcriptional activation of C-6 and S-23. AR binding affinity was determined using a radioligand competitive assay. The ability of compound of interest to induce AR-mediated transcriptional activation was determined using a cotransfection assay in CV-1 cells. The transcriptional activity induced by each compound at a concentration of 10 nm was reported as the percentage of that observed for 1 nm DHT. Each value represents the mean ± sd of three replicates. *, Data were reported by Chen et al. (13).

Figure 2

A, The androgenic activity and anabolic activity of S-23 in castrated male rats. S-23 was administrated to animals via daily sc injections for 14 d with doses ranging from 0.01 to 3 mg/d. All organ weights were normalized with body weight and presented as the percentage of intact control. Each bar represents the mean ± sd of five rats. I and C, Significant difference from intact control and castrated control groups analyzed by single-factor ANOVA with P < 0.05 followed by Dunnett’s multiple comparison test. B, Dose-response curves of S-23 in castrated male rats. Emax and ED₅₀ in this figure were obtained by nonlinear least-square regression analysis. Each value represents the mean ± sd of five rats. C, The androgenic activity and anabolic activity of S-23 in intact male rats. S-23 was administrated to animals via daily sc injections for 14 d with doses ranging from 0.01 to 1 mg/d. All organ weights were normalized with body weight and presented as the percentage of intact control. Each bar represents the mean ± sd of five rats. *, Significant difference from the vehicle-treated, intact control group analyzed by single-factor ANOVA with P < 0.05 followed by Dunnett’s multiple comparison test. ORX, Castrated.

Figure 3

Mean plasma concentration-time profile of S-23 in male rats. Plasma concentrations of S-23 were measured using HPLC. Data were expressed as microgram per milliliter, and each point represents the mean ± sd (n = 4 or 5/group).

Figure 4

Testicular sperm concentrations. Each bar represents the mean ± sd (n = 5 or 6/group). The letters I and E above each error bar represent a significant difference between the group and intact control group and estrogen-treated group, respectively, as analyzed by single-factor ANOVA followed by Dunnett’s multiple comparison test with P < 0.05.

Figure 5

The linear correlation between the dose rate of S-23 and body composition (percent of FM and percent of fat free mass). Each value represents the mean ± sd (n = 5 or 6/group). *, Significant difference between the group and estrogen-treated group, as analyzed by single-factor ANOVA followed by Dunnett’s multiple comparison test with P < 0.05.